Wheat in the Pacific Northwest of the USA is damaged by one or more soilborne diseases including take-all, caused by Gaeumannomyces graminis var. tritici and Rhizoctonia root rot, caused by Rhizoctonia solani AG-8 and R. oryzae. These two diseases often occur as a complex in the same field and their incidence and severity are exacerbated by direct seeding (no-till) and intensive cereal production (see e.g., Paulitz, T. C., et al. 2002. Can. J. Plant Pathol. 24:416-428). Commercial wheat varieties have no resistance to either of these diseases and chemical treatments perform inconsistently (see e.g., Cook, R. J. 2003. Physiol. Mol. Plant Pathol. 62:73-86). Biological control with strains of fluorescent Pseudomonas spp. and Bacillus spp. applied as seed treatments have provided significant suppression of take-all (see e.g., Pierson, E. A., and Weller, D. M. 1994. Phytopathology 84:940-947; Weller, D. M., and Cook, R. J. 1983. Phytopathology 73:463 469) and Rhizoctonia root rot (see e.g., Cook, R. J., et al. 2002. Plant Dis. 86:780-784; Kim, D.-S., et al. Phytopathology 87:551-558).
Many microorganisms have been developed for commercial use and their effectiveness continues to improve (see e.g., Kloepper, J. W., et al. 2004. Phytopathology 94:1259-1266; Weller, D. M. 2007. Phytopathology 97:250-256). However, despite these successes, inconsistent performance remains a barrier to the broader use of biocontrol agents for the control of root diseases of wheat and other crops. A treatment may provide significant control in one field or season but not the next. Approaches to improve biocontrol performance have included the application of larger or multiple doses of bacterial inoculum, the development of new formulations (see e.g., Schisler, D. A., et al. 2004. Phytopathology 94:1267-1271), the use of strain combinations (see e.g., Kloepper, J. W., et al. 2004, supra; Pierson, E. A., and Weller, D. M. 1994, supra), and strain improvement by genetic engineering or the transfer of “biocontrol genes” to recipient strains with other desirable attributes (see e.g., Delany, I. R., et al. 2001. Plant Soil 232:195-205; Huang, Z., et al. 2004. FEMS Microbiol. Ecol. 49:243-251; Timms-Wilson, et al. 2000. Mol. Plant-Microbe Interact. 13:1293-1300).
Thus, what is needed in the art are improved microbial strains which provide effective and consistent biocontrol of soilborne root diseases of wheat and other crops.
Fortunately, as will be clear from the following disclosure, the present invention provides for these and other needs.